Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.50   6.137%   $193.7   $193.70   $193.70   $193.70  
  Purchase #2 $63.88   13.544%   $72.5319   $72.53   $72.55   $72.50  
  Purchase #3 $150.96   6.424%   $160.6577   $160.66   $160.65   $160.70  
  Purchase #4 $205.33   4.190%   $213.9333   $213.93   $213.95   $213.90  
  Purchase #5 $149.26   9.600%   $163.589   $163.59   $163.60   $163.60  
  Purchase #6 $43.79   10.167%   $48.2421   $48.24   $48.25   $48.20  
  Purchase #7 $242.33   4.463%   $253.1452   $253.15   $253.15   $253.10  
  7 purchase totals = $1,038.05       $1,105.7992   $1,105.80   $1,105.85   $1,105.70